1. The Field of the Invention
The present invention is directed generally to a method for controlling external recirculation and water heater temperature setpoint. More specifically, the present invention is directed to a method for controlling external recirculation and temperature setpoint of a water heater.
2. Background Art
In a water heating system serving a large number of customers in a building, e.g., hotel, apartment complex, restaurant, high rise, industrial complex, a single large water heating system or multiple units of functionally networked water heating systems are traditionally used to service the many hot water demands of occupants of the building. In delivering hot water to far reaches of a building, one or more centrally located water heaters are typically configured to deliver hot water via long stretches of insulated or non-insulated fluid conductors. Considerations are typically made to account for heat losses (to the fluid conductors and their surroundings) when delivering hot water over great distances, e.g., hot water prepared to a higher setpoint temperature is provided to account for temperature drop due to heat losses on its path to points of use. In one example, for a typical hot water delivery temperature of 120 degrees F., the setpoint temperature of the hot water heater is adjusted to 140 degrees F. such that the delivery temperature can be kept at about 120 degrees F. In most installations, points of use are not equipped with temperature sensors for temperature feedback. Therefore, such a system operates with an assumption that the delivery temperature is inadequate if the water heater temperature setpoint is not increased. It is therefore clear that significant energy inefficiencies can result from such a system when water delivery is requested. It is also customary to keep the hot water at or near points of use at suitable delivery temperature using an external recirculation circuit at all times to anticipate a hot water usage. Therefore, energy wastage occurs not only during periods of use of hot water but also when a usage is expected to occur or periods of no use. It may also be customary to equip a hot water delivery system with an external recirculation circuit which is aided with a dedicated pump. In conventional systems, this dedicated pump is turned on at all times with or without a hot water demand. If hot water has already been demanded, the external recirculation circuit already contains sufficient warm water and therefore should not require that the dedicated pump to still be run. Therefore, significant amounts of energy is lost by the practice of constantly pushing water through the external recirculation circuit regardless of whether a demand exists and that the delivery temperature be constantly maintained at a higher level in anticipation of temperature losses at points of delivery regardless of whether a demand exists.
Thus, there is a need for a method for determining the periods in which external recirculation are unnecessary and the periods in which the setpoint temperature of a water heating system can be lowered such that energy may be conserved during these periods by turning off the external recirculation and lowering the setpoint temperature of the water heaters.